The present invention relates to the compositions of associating polymer protective barrier films which will protect materials, such as agricultural chemicals, for a period of time and then degrade and release the encapsulated contents to the environment. More specifically, this invention relates to the preparation of ionomer compositions containing compatibilized polymers which will be degraded by microorganisms.
It is extremely important today to find an effective means of degrading polymeric materials, which are used in packaging and agricultural films. In the case of mechanical goods, the pollution problem is becoming more severe as used plastic bottles, containers, wrapping film, sheet, etc. accumulate in garbage dumps, along shores, in rivers and other places. There is a great need for some sort of degrading system that will allow the plastic to have a useful life, after which the plastic will degrade into a material that can be handled easily. In other film applications, controlled release of encapsulated materials requires environmental degradation.
This invention provides new polymeric systems capable of degrading to a crumbly friable mass. These systems are based on the ability to produce compatible polymeric films from sulfonated polymers and amine terminated polycaprolactone. The sulfonated polymer can be in the free acid form or neutralized with a metal which can coordinate with the amine. The combination makes excellent coatings, films and mechanical goods due to the compatibilization of the multiple polymer blend. The degradability comes from the inherent characteristic of polycaprolactone, susceptibility to biodegradation.
The advent of plastics has introduced improved methods of packing goods. For example, polyethylene and polypropylene films, bags and bottles and polystyrene foam cups have the advantages of being chemically resistant, mechanically tough, light in weight and inexpensive. However, the increasing use of plastics in packaging has led to the appearance of such materials in litter. While littered plastic articles are no more objectionable than littered articles of other materials, such as paper objects and metal cans, it has been suggested that the impact of plastic litter can be minimized by the development of plastic materials capable of undergoing chemical degradation upon exposure to the natural environment.
Several approaches to the enhancement of the environmental degradability of plastics have been suggested. These include: (1) the incorporation of particulate biodegradable materials, such as starch, as "fillers"; (2) the introduction of photodegradation-sensitizing groups into the molecular structure of a polymer by copolymerization of a common monomer with a second monomer processing such groups; and (3) the incorporation of small amounts of selected additives which accelerate oxidative and/or photo-oxidative degradation. The last approach is particularly attractive for the following reasons. First, the physical properties of the additive-containing composition are extremely similar to those of the base polymer. Second, existing compounding and fabrication processes and equipment can be utilized in the manufacture of finished products; hence, the cost of the finished product should be relatively low. Third, the sensitivity of the composition to environmental degradation can be controlled by proper selection of the type and concentration of additive(s).
The enhancement of the rate of environmental deterioration of plastics through the use of oxidation-promoting additives is known in the prior art. For example, the preparation of degradable polyolefin films containing certain organic derivatives of transition metals is described in U.S. Pat. No. 3,454,510.
Various type additives have been employed in plastic film in order to make the plastic film biodegradable. For example, in U.S. Pat. No. 4,224,416 auto-oxidizable amines are employed. In U.S. Pat. No. 3,994,855 a photolyzable metal compound is employed. U.S. Pat. No. 4,495,311 employs an additive system consisting of a metal compound having at least two valence states and a benzoyl derivative of an organic compound.
The present invention describes a polymer system which is biodegradable in film form. The polymer system of the instant invention comprises a compatible mixture of a sulfonated polymer with an amine terminated polycaprolactone. Compatible mixtures of sulfonated elastomeric polymers and amine terminated polycaprolactones are described in U.S. Pat. No. 4,421,898; however, U.S. Pat. No. 4,421,898 failed to teach or recognize the use of these polymer mixtures in their film form as an agricultural mulch.